(Supported by NIEHS Superfund ESO4913 to D. Carpenter). The adsorption of polychlorinated biphenyls (PCB's) onto river clay depends upon the size of the clay particle, the type of particles (elemental analysis) and the geometry of the particles. HVEM and IVEM were used to determine the clay particle size, the elemental composition and the shape. We hope to be able to locate the actual PCB adsorption sites on the particles in the future. Using the IVEM, energy-dispersive X-ray microanalysis spectra and digital micrographs were taken of particles of St. Lawrence river clay containing PCB's. Cryo-EM was used to retain the volatile PCB's. Then the HVEM was used to provide improved images of the larger particles analyzed by the IVEM, and wide-field overviews of the analysis areas. The results were presented at Microscopy and Microanalysis '98 in August. Tivol, W.F., Casey, A.C., Liu, X-M, Bush, B. (1998) Binding of polychlorinated biphenyls to sediment. Microscopy and Microanalysis Vol 4, suppl. 2 (Proc. Microscopy and Microanalysis '98) Ed. G. Bailey, et al., Springer , New York, pp. 498-499.